1. Field of the Invention
The present invention relates to a control process for a piezoelectric pump of an electric household appliance comprising a pump chamber equipped with a mobile wall displaceable under the action of a piezoelectric actuator, and to an electric household appliance comprising a piezoelectric pump electrically powered by a circuit employing such a control process.
2. Brief Description of the Prior Art
An electric circuit for a piezoelectric pump supplying power to the pump directly, at the frequency of the electric main, is disclosed in French patent #2 929 450 filed by the applicant. Such a supply circuit has the advantage of being dependable and inexpensive to use. However, a disadvantage resides in such a circuit in that it does not enable the pump flow rate to be modulated, in particular reduced.
Reducing the flow rate of the pump by acting upon the voltage on the terminals of the piezoelectric actuator is known to the prior art, wherein a reduction of the voltage makes it possible to obtain a lesser deformation of the piezoelectric actuator and hence a reduction of the volume swept by the mobile wall during an alternation of the electric signal. However, a disadvantage resides in the reduction of the voltage in that it reduces the pump compression rate, i.e., the ratio between the volume swept by the mobile wall and the dead volume of the pump chamber. Lowering the pump compression rate below a predetermined threshold leads to problems in the auto-priming of the pump and/or in the expulsion of air bubbles present in the pump chamber.
Reducing the flow rate of a piezoelectric pump by lowering the frequency of the electric signal on the terminals of the piezoelectric actuator in such a way that a lesser volume is swept by the mobile wall within a given time period is likewise known to the prior art. However, a disadvantage resides in such a solution in that it requires a frequency modulation circuit, which is relatively expensive to manufacture. Furthermore, lowering the frequency of the supply signal also has the disadvantage of reducing the displacement speed of the mobile wall to a rate that is no longer adequate for the proper expulsion of any air bubbles present in the pump chamber.